Hearing

i subscribe to a newsletter from occupationalhazards.com because it has some good safety information that i'm not aware of every now and again. this week there was a blurb from a company about radio headsets. i thought it was interesting so here it is.

When headset radios first appeared in stores several decades ago, they were not marketed as hearing protectors – a good thing, since they offered very little attenuation of noise. At some frequencies, the headsets were even found to amplify background noise (with the radio turned off) due to resonance in the earcup. To be a hearing protector, an earmuff must be designed to be a hearing protector from the start.

The volume settings of typical portable stereo headsets have been measured at 81 dBA at 50 percent volume setting, 91 dBA at 75 percent volume, and 96 dBA at 100 percent volume--a hazardous noise level if listened to continuously for several hours. Ideally, a radio headset should allow the enjoyment of music at safe levels, but also reduce the background disturbance in a noisy environment.

Today's new hearing protectors do just that: built-in radios contain circuitry that limits their maximum radio volume. When the radio is turned on, the sound output is electronically limited to 82 dB. The noise level of the radio will certainly fluctuate (even though there is an 82 dB peak cutoff in the circuitry, the average noise level of the signal may be much lower). But for the sake of the following example, let's just assume the worst-case radio noise--a constant noise level of 82 dB from the radio worn in a noise environment of 90, 100 and 105 dB.

When two noise sources are added together, the decibels are added logarithmically, not arithmetically. This means that the sum of two identical sound sources (90 dB + 90 dB) would sum to equal 93 dB. Using a logarithmic calculator, let's determine the effective exposure for 90, 100 and 105 dB of environmental noise, with an assumed 20 dB of attenuation from the earmuff, and constant radio signal of 82 dB:

Total Effective Exposure for a Radio Earmuff Worn in 90, 100 and 105 dB of Noise

Noise Level	90dB		100dB		105dB
Attenuation	-20dB		-20dB		-20dB
Passive Exposure	70dB		80dB		85dB
Plus Radio Noise	+82dB		+82dB		+82dB
Effective Exposure	82dB		84dB		87dB

Since the radio output is limited to a safe 82 dB maximum, the radio adds very little noise to effective exposures in high noise levels. In a high-noise job that is also repetitive or monotonous, a radio earmuff can add significantly to worker satisfaction and enjoyment, without sacrificing hearing protection.

Brad Witt, MA, CCC-A, is audiology and regulatory affairs manager for Bacou-Dalloz Hearing Safety Group.